1. Field of the Invention
This invention relates to a venturi for a watercraft vehicle, and more particularly to a novel venturi for varying the surface area of the water flow exiting the venturi, and a means for adjusting the surface area of the exiting water flow between alternative riding conditions.
2. Discussion of Related Art
Venturis and exit nozzle apparatuses for watercraft vehicles conventionally comprise components which are mounted to the venturi or nozzle for directing the flow of the exiting water. Typically, the flow direction apparatus comprise rotatable nozzles or deflectors within the nozzles for moving the exiting water in a particular direction. In general, the rotatable nozzles may be adjusted in vertical or horizontal directions. Accordingly, it has become common practice in the art for an exit nozzle or venturi of a jet pump for various watercraft vehicles to contain attachments thereon for directing the flow of the water exiting the jet pump and to thereby control the direction of travel for the vehicle.
Several fluid flow directing apparatuses for venturis and exit nozzles of watercraft vehicles, as well as other types of vehicles, have been patented. The nozzles disclosed in the Prior Art comprise means for controlling the direction of the fluids exiting the nozzles, thus controlling the direction of travel of the vehicle. However, none of the patents disclose a single means for affecting the thrust and acceleration of the vehicle by controlling the surface area of the water exiting the venturi. Furthermore, the Prior Art fails to disclose modifications to the velocity of the water exiting the venturi which affects the performance of the vehicle. The venturi functions to accelerate the water as it exits the stator vanes of the impeller of the jet propulsion unit. Based upon principles of classical physics, it is known that reducing the circumferential size of the venturi to accelerate the same amount of water as a standard size venturi will cause the acceleration of the water to increase. It has been determined that by changing the circumferential size of the exit orifice of the venturi, the thrust and velocity of the exiting water is affected.
For example, a wider diameter venturi exit orifice will decrease back pressure in the jet propulsion unit, and will allow a higher mass flow of water to be processed through the jet propulsion unit more rapidly while reducing the pump torque required. However, a larger diameter venturi exit orifice will cause a loss of top speed due to a reduced velocity of the water exiting the venturi. In comparison, if we select a venturi with a smaller exit orifice, the back pressure to the jet propulsion unit will increase. As a result, a lower mass flow of water is processed, but the velocity of the water exiting the venturi increases. This allows the vehicle to achieve higher speed, but does not provide the quantity of water necessary for good acceleration of the vehicle. Accordingly, different size exit orifices are a compromise for providing the best combination of acceleration and top speed for the vehicle.
Therefore, what is desirable is a novel venturi or nozzle for a jet propulsion unit for a watercraft vehicle having a means for adjusting the diameter of the water at a distal end of the venturi, wherein the velocity of the exiting water is variable among several different positions so that the thrust and acceleration allows the vehicle to achieve maximum top end speed in one configuration of the venturi and provides an improved acceleration with reduced power required from the jet propulsion unit in an alternative configuration.